It is becoming increasingly more common for wheelchair wheels to be provided with gears in order to facilitate the use of wheelchairs by different users, especially when travelling on surfaces having varying gradients. This is especially the case for wheels intended to be used on manually powered wheelchairs.
These manually powered wheelchairs are propelled, steered and braked by a user by either turning or gripping a ring attached to each of the two main wheels of the wheelchair. By providing a gear mechanism between the gripping ring and the wheelchair wheel, the rotational speed of the gripping ring can differ from the rotational speed of the wheelchair wheel, which, for example, enables the user to reduce or increase the number of gripping ring actions for travelling a given distance. Typically, a user may want to reduce the number of gripping ring actions when travelling on smooth surfaces and in easy and flat terrain, whereas a user may want to increase the number of gripping ring actions when travelling in hard terrain and/or uphill.
The advantages of providing a wheelchair wheel with a gear mechanism have been recognized in several patent applications. For example, U.S. Pat. No. 6,805,371 to Meginniss, III et al. discloses a two-gear arrangement for a wheelchair wheel, comprising a shift bar, which, when a user wants to shift gear, is moved perpendicularly to the wheelchair axle and through a housing, which contains a gear assembly and which is mounted on the outside of the wheelchair wheel. A disadvantage with this arrangement is that it—since it can be characterized as an outside or external gear-shift arrangement—adds to the overall width of the wheelchair. An external gear-shift arrangement can also be said to inherently have a larger moment of inertia than an internal gear-shift arrangement.
In U.S. Pat. No. 5,482,305 to Jeffries et al. a gear assembly within a hub is disclosed, which comprises a disc-shaped shifter, the turning of which causes a shift pin to move in a helical slot provided in a tubular sleeve arranged at the end of the main wheel axle and to move axially in an elongated linear slot in the main wheel axle, to accomplish coupling to direct drive mode and to lower-gear mode via a planetary gear system, respectively. To achieve enough axial shifting movement within the limited space provided within the interior of the wheel assembly hub, the pitch of the helical sleeve is high (large), meaning that considerable force has to be exercised by a user on the relatively small disc-shaped shifter in order to shift gear.
Although the gear-shift mechanisms disclosed in the patents listed above fulfill the intended purpose of providing a gear-shift arrangement for a wheelchair wheel, they are still associated with disadvantages, not least from a user's perspective when it comes to user-friendliness and maneuverability. A general object of the present invention is therefore to provide an improved gear-shift arrangement for a wheelchair wheel, which is easy to operate and which not unnecessarily adds to the overall width of the wheelchair wheel and thereby to the width of the wheelchair. Another object of the present invention is to provide an improved gear-shift arrangement which, with maintained operability and user-friendliness, easily can be adapted to a multi-gear arrangement comprising more than two gears. A further object of the invention is to provide a gear-shift arrangement, which in a reliable way can be operated by a minimum amount of force.